This invention relates to curtain doors for use at the charge or exit ends of a metallurgical reheat furnace. It relates specifically to curtain doors which include at least two metal mesh curtains of unequal lengths and a separate insulating and door sealing means positioned between the furnace opening and metal mesh curtains to provide a furnace door which, when lowered to its closed position, is adaptable to stock of varying thickness with minimum heat loss from the reheat furnace.
In the past, furnace doors comprised either hinged solid doors for small furnaces, vertical lifting solid doors for large furnaces, or, in the case of smaller furnaces where doors would be open most of the time due to operators adding, rearranging or removing stock, chain doors were substituted for solid doors.
The vertical lifting solid doors used on the larger furnaces consist of reinforced frames lined with firebricks. Such doors are extremely heavy, difficult to operate and are subjected to various types of mechanical and thermal abuses. For example, it is common to have stock catch the bottom edge of such a door, pull it away from the furnace, and then drop it back against the door seats. Additionally, because doors are made to be opened and closed, they are subjected to constant thermal changes and the firebricks are cooled when the door is opened and reheated when the door is closed. Such treatment of furnace doors causes spalling and loosening of the firebricks and the loosened firebricks tend to catch on the furnace front and making it very difficult to raise or lower the furnace door. As a result, operators tend to keep furnace doors in a raised position, which causes furnace heat loss, higher operating costs and dangerously exposes furnace operators to extremely high temperatures.
In order to overcome the aforementioned problems related to the vertical lift solid doors which are currently in use on large reheating furnaces, a furnace door must be provided which is relevantly light in weight, unaffected by thermal variations, inexpensive to maintain and convenient for the furnace operators to use.